excelTime 用于excel 导入日期格式

function excelTime($days, $time=false,$str='-'){
    if(!$days)return false;
    if(function_exists("gregoriantojd")){
	if(is_numeric($days)){
		//based on 1900-1-1
		$jd = gregoriantojd(1, 1, 1970);
		$gregorian = jdtogregorian($jd+intval($days)-25569);
		$myDate = explode('/',$gregorian);
		$myDateStr = str_pad($myDate[2],4,'0', STR_PAD_LEFT)
				.$str.str_pad($myDate[0],2,'0', STR_PAD_LEFT)
				.$str.str_pad($myDate[1],2,'0', STR_PAD_LEFT)
				.($time?" 00:00:00":'');
		return $myDateStr;
        }
	}else{
     $date=$days>25568?$days+1:25569;
     $ofs=(70 * 365 + 17+2) * 86400;
     $days =  date("Y".$str."m".$str."d",($date * 86400) - $ofs).($time ? " 00:00:00" : "");
    }
	return $days;
}